There are many circumstances in which a head end or source router cannot accurately determine the end-to-end cost and/or possibly other metrics associated with a path that is used to establish an end-to-end PseudoWire (PW). This is especially true for Multi-Segment PWs (MS-PWs) or for PWs spanning multiple operational or administrative domains such as routing domains. Although a head-end router might attempt to find the best path based on its local information, there is no guarantee that the established path is optimal with respect to the above mentioned metrics. There are currently no mechanisms for re-optimizing virtual connections such as end-to-end PWs based on the total end-to-end cost discovered.
In Asynchronous Transfer Mode (ATM) systems, a Domain Based Rerouting feature together with other signalling capabilities of Private Network-Network Interface (PNNI) specifications has been used to collect a total cost of a head-end routed connection, to establish alternative connections, and then to move one connection into another, potentially optimizing the end-to-end cost. This particular feature, however, is currently limited to ATM, and is also not applicable to communication systems in which centralized path computation is deployed, for example.
In Internet Protocol (IP) networks, external systems are typically required to re-optimize paths. However, these external systems likely have a limitation of working within a single administrative boundary only, as security concerns tend to prevent network operators from sharing their network topology information so as to allow effective end-to-end optimization.
Thus, there remains a need for improved techniques relating to optimization of, and more generally selection between multiple available paths or routes for, virtual connections such as PWs.